Electrical connecting structure for electrically connecting terminals to each other

ABSTRACT

A connection terminal portion of a substrate and a terminal portion of an external circuit substrate or a terminal portion of a part are electrically connected together using an anisotropic electrically conducting film. A structure in which a first substrate having a connection terminal portion and a second substrate having a connection terminal portion or a connection terminal portion of a part are connected together with an anisotropic electrically conducting adhesive containing electrically conducting particles, wherein the thickness of the electrically conducting film provided for the connection terminal of the first substrate, the second substrate or the part is smaller than the diameter of the electrically conducting particles. The invention is further concerned with a method of accomplishing the electrical connection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrically connecting structureand a method of electric connection. More specifically, the inventionrelates to an electrical connection using an electrically conductingadhesive.

2. Description of the Related Art

Referring, for example, to Japanese Unexamined Patent Publication(Kokai) No. 52-70369, a connection terminal portion of a substrateprovided on a glass substrate which is a liquid crystal panel and aterminal portion of an external circuit substrate are electricallyconnected together by disposing an electrically conducting rubberbetween the connection terminal portion of the substrate and theterminal portion of the substrate for connection to an external circuit,involves problems in regard to the assembling operation efficiency sincethe electrically conducting rubber must be incorporated at a specifiedposition and lack of stability in the contact between the electricallyconducting material in the electrically conducting rubber and theterminal portions.

In order to solve the above-mentioned problems, therefore, there hasbeen proposed technology which uses an anisotropic electricallyconducting adhesive containing electrically conducting particles insteadof using an electrically conducting rubber.

As for means of using an isotropic electrically conducting adhesivedisclosed in the aforementioned Japanese Unexamined Patent Publication(Kokai) No. 52-70369, furthermore, Japanese Unexamined PatentPublication (Kokai) No. 58-115779 discloses, by way of numericalfigures, a concrete example of electrically connecting a connectionterminal portion of a substrate and a terminal portion of an externalcircuit substrate by using an anisotropic electrically conducting film.

In order to impart electric conduction to parts having low heatresistance such as liquid crystal panels and the like, an anisotropicelectrically conducting adhesive has been much used in recent years astaught by the aforementioned prior art. Referring, for instance, toFIGS. 7 and 8 which are diagrams explaining the prior art, electrodes 33and electrodes 41 are formed on the facing surfaces of a pair ofsubstrates 30 and 40 that are disposed in facing manner, a connectionterminal portion 31 of the electrodes 33 and a connection terminalportion (not shown) of the electrodes 41 are disposed on the outside ofa sealing portion 50, and liquid crystals are sealed inside the sealingportion 50 to constitute a liquid crystal display device.

A prior art will now be explained with reference to FIGS. 8 and 9 whichare views of a liquid crystal display device along the line A--A of FIG.7. In FIGS. 8 and 9 which are sectional views along the line A--A ofFIG. 7 of prior art, on the upper surface of the substrate 32constituting the liquid crystal display device is disposed a connectionterminal portion 31 that electrically couples the liquid crystal paneland the external circuit together, and the electrode composed of anindium tin oxide (ITO) film is disposed on the connection terminalportion 31 and on the pixel unit of the liquid crystal panel in whichthe liquid crystals are filled. Furthermore, a film-like electricallyconducting sheet (hereinafter referred to as FPC) 10 is arranged facingthe connection terminal portion 31 of the substrate 30.

Note that the FPC is usually formed in a film like configuration andthus it is generally used as an adhesive material, by being insertedinto a space formed between two opposite electrodes. The FPC 10 isobtained by forming a copper pattern 13 which is an electricallyconducting wiring pattern of copper or the like on a base film composedof a polyimide or the like, and applying a film of solder or tin of athickness of 4 to 6 μm onto the copper pattern 13 by electroplating. Aportion constituted by the electrically conducting film 14 and thecopper pattern 13 of FPC 10 facing the connection terminal portion 31 ofthe substrate 32 is referred to as connection terminal portion 11. Theconnection terminal portion 11 and the connection terminal portion 31are disposed facing each other with an anisotropic electricallyconducting adhesive 20 which is an anisotropic electrically conductingfilm being disposed therebetween. The anisotropic electricallyconducting adhesive 20 is constituted mainly by electrically conductingparticles 21 and a resin binder 22. In general, the electricallyconducting particles 21 comprise beads made of epoxy resin orpolystyrene resin, and plated with nickel and gold, and the resin 22, ingeneral, is an epoxy resin.

When a conventional anisotropic electrically conducting adhesive, e.g.,CP7131, produced by Sony Chemical Co. is used, the electricallyconducting particles having an average diameter of about 6 μm, and thethickness of the anisotropic electrically conducting adhesive 20 beforebeing adhered with the application of heat and pressure is about 25 μm.On the other hand, the copper pattern 13 at the terminal portion 11disposed on the FPC 10 has a thickness of 35 μm, and the electricallyconducting film 14 formed on the copper pattern 13 has a thickness ofabout 6 μm. Moreover, the connection terminal portion 33 disposed on thesubstrate 30 is composed of ITO.

Here, the anisotropic electrically conducting adhesive 20 that hasheretofore been used for accomplishing electric connection comprises,for example, an epoxy resin as a main component, the epoxy resin beingmixed with capsules containing a suitable curing agent and being furthermixed with hard electrically conducting particles such as theaforementioned resin beads. The anisotropic electrically conductingagent 20 is filled in a gap between the two facing connection portions,for example, between the electrodes. When the anisotropic electricallyconducting agent 20 is treated with the application of heat of atemperature of, for example, 170° to 180° C. and a pressure of, forexample, 40 kg/cm² in a direction in which the length of gap formedbetween the pair of facing electrodes decreases, then, the capsules aredestroyed, the curing agent is cured upon reacting with the epoxy resinthat is the chief component of the adhesive agent. As a result, theelectrically conducting particles and the two electrodes are connectedto each other, establishing the electric connection in only a directionin which the pressure is applied.

When the thermosetting resin such as the epoxy resin or the like iscured, thermal energy or ultraviolet radiation can also be used so as tocure the thermosetting resin, instead of the above-mentioned capsules.

According to the above-mentioned prior art as shown in FIG. 8, adhesionis accomplished with the application of heat and pressure from thedirection of arrow Y in order to accomplish the electric conductionbetween the connection terminal portion 31 of the substrate 30 and theconnection terminal portion 11 of the FPC 10 via the electricallyconducting particles 21 and to firmly adhere the FPC 10 and thesubstrate 30 together. Being adhered with the application of heat andpressure, the resin moves toward the direction where the internalpressure is low between the FPC 10 and the substrate 30. Here, theelectrically conducting particles 21 have poor fluidity and change theirpositions little and remain between the electrically conducting film 14of the connection terminal portion 11 and the ITO 33 disposed on theconnection terminal portion 31 thereby to establish electric conductionbetween the electrically conducting film 14 and the ITO 33. However, thepresent inventors have found the fact that when the adhesion isaccomplished with the application of heat and pressure from thedirection of arrow Y in FIG. 8, the electrically conducting particles 21are buried in the electrically conducting film 14 as shown in FIG. 9since the electrically conducting film 14 of FPC 10 is composed of asolder or a tin film having a thickness of about 6 μm, the electricallyconducting particles 21 have an outer diameter of about 6 μm, and theITO 33 of the substrate 10 is composed of indium tin oxide. Accordingly,the electrically conducting particles lose their action to a conspicuousdegree, whereby the conduction resistance increases and poor conductionoccurs causing the conduction to be interrupted.

When a connection terminal portion 20 of a data processing circuit 40,for example a liquid crystal display device, including electrodes 33 and41 and a suitable connection terminal 10 connected to an externalcontrol circuit (not shown) are connected together according to theprior art as shown in FIGS. 7 to 9, a digital control signal is fed fromthe control circuit to the connection terminal portion 20 of the dataprocessing circuit 40 via the connection terminal 10, and ON or OFFlevel of the digital signal can be discriminated even when theconnection resistance of the connection portion is high to some extent.In the field of liquid crystal technology in recent years, however, adata transfer device has been developed in which a data processingcircuit and a drive circuit means for driving the data processingcircuit are formed on the same glass substrate. In such a data transferdevice, a signal for controlling the drive circuit means is, in manycases, an analog signal that is input from a control circuit outside theglass substrate via wiring.

In the above-mentioned data transfer device, therefore, it becomesdifficult to reliably and correctly discriminate a change in the analogsignal unless the resistance is decreased in the connection portionbetween the control circuit and the drive circuit means. It has,therefore, been desired to decrease the connection resistance.

On the other hand, in a liquid crystal display panel called a chip onglass (COG) type panel, in which an integral circuit (IC), for drivingthe liquid crystal display panel, is mounted on a transparent substrateof the panel, electrical power for driving the IC should be applied tothe connecting terminal portions and thus a large amount of current mayflow through the connecting terminal portions connected to the powersource. Therefore, it is naturally required that the connectionresistance should be reduce as much as possible.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an electricallyconnecting structure which is free from defects inherent in theabove-mentioned prior art, is simple in constitution, and reliablyexecutes a connection, the electrically connecting structure beingcapable of maintaining a low connection resistance at the connectionportion.

In order to accomplish the above-mentioned object, the electricallyconnecting structure according to the present invention basicallyemploys the constitution that is described below.

That is, in a data transfer device constituted by, at least, a dataprocessing circuit equipped with a plurality of electrically conductingterminal groups and a drive circuit means connected to a plurality ofelectrically conducting terminals in the data transfer device, anelectrically connecting structure characterized in that a connectionportion is formed between the facing connection terminal portions of thecircuits or between the connection terminal portion of the circuit andthe connection terminal portion of an external input circuit meansfacing thereto, the connection portion having space formed by the twofacing electrodes which is filled with an anisotropic electricallyconducting adhesive containing electrically conducting particles, thesurface of at least one of the electrodes being coated with anelectrically conducting film, an electrically conducting passage beingformed between the two facing electrodes directly by said electricallyconducting particles or by an indirect junction via the electricallyconducting film, and the total thickness of the electrically conductingfilms being smaller than the minimum diameter of the electricallyconducting particles. More concretely speaking, the invention isconcerned with a data transfer device such as a liquid crystal displaydevice, for example, in which, at least, a data processing circuitequipped with a plurality of electrically conducting terminal groups anda drive circuit means which connects to a plurality of electricallyconducting terminals in the data transfer circuit, are formed on thesame glass substrate, wherein an electrically connecting structure ischaracterized in that a connection portion is formed between the facingconnection terminal portions of the circuits or between the connectionterminal portion of the circuit and the connection terminal portion ofan external input circuit means facing thereto, the connection portionhaving space formed by the two facing electrodes and is filled with ananisotropic electrically conducting adhesive containing electricallyconducting particles, the surface of at least one of the electrodesbeing coated with an electrically conducting film, an electricallyconducting passage being formed between the two facing electrodesdirectly by said electrically conducting particles or by an indirectjunction via the electrically conducting film, and the total thicknessof the electrically conducting films being smaller than the minimumdiameter of the electrically conducting particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a sectional view illustrating a first embodiment of thepresent invention; and FIG. 1(B) is a sectional view illustratinganother example of the first embodiment as mentioned above;

FIG. 2 is a sectional view illustrating a second embodiment of thepresent invention;

FIG. 3 is a sectional view illustrating a third embodiment of thepresent invention;

FIG. 4 is a sectional view illustrating a fourth embodiment of thepresent invention;

FIG. 5 is a sectional view illustrating a fifth embodiment of thepresent invention;

FIG. 6 is a sectional view illustrating a sixth embodiment of thepresent invention;

FIG. 7 is a diagram showing the appearance of a liquid crystal displaydevice;

FIG. 8 is a sectional view of before the connection is accomplished bythe application of heat and pressure according to a prior art;

FIG. 9 is a sectional view of after the connection is accomplished bythe application of heat and pressure according to the prior art;

FIG. 10 is a diagram showing a connecting configuration of theelectrically conducting film in the connection portion in theelectrically connecting structure;

FIGS. 11(A) and (B) are cross-sectional views of the electricallyconducting particle used in the present invention;

FIGS. 12(A) and (B) are enlarged cross-sectional views of a constructionof the connecting portion of one embodiment of the present invention;and

FIG. 13 is an enlarged photograph showing a plane view of the connectingportion of the present invention which is formed by FPC after removingthe electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electrically connecting structure and the method of fabricationthereof according to the present invention will now be described indetail by way of embodiments with reference to the drawings.

FIG. 1(A) is a sectional view illustrating a concrete constitution of anelectrically connecting structure according to the present invention.That is, in a data transfer device 1 constituted by, at least, a dataprocessing circuit 100 having a connection portion 20 equipped with aplurality of electrically conducting terminal groups 31 and a drivecircuit means 200 which is connected to the terminals 31 and separatelyselects a plurality of electrically conducting terminals 31 in the dataprocessing circuit 100 and sends predetermined signals to said dataprocessing circuit 100, and electrically connecting structure ischaracterized in that a connection portion S is formed between thefacing connection terminal portions 13 and 31 of the circuits 100 and200. The connection portion S having a gap G formed by the two facingelectrodes 31 and 13 and is filled with an anisotropic electricallyconducting adhesive 22 containing a plurality of electrically conductingparticles 21, the surface of at least one of the electrodes, e.g., theelectrode 13 being coated with an electrically conducting film 14, anelectrically conducting passage being formed between the two facingelectrodes 31 and 13 directly by said electrically conducting particles21 or indirectly by junctions P, P' via the electrically conducting film14, and the total thickness of the electrically conducting film 14 beingsmaller than the minimum diameter of the electrically conductingparticles 21.

According to the present invention, furthermore, the data processingcircuit 100 and the drive circuit 200 may be formed on the same glasssubstrate 32, or they are mounted on a separate glass substrate,respectively.

In the structure of the present invention in which the first substrate32 having a connection terminal portion 20 and the second substrate forexample, FPC including IC or the like 12, having a connection terminalportion 200, different from the first substrate, are connected to eachother using the anisotropic electrically conducting adhesive 22containing electrically conducting particles 21, the electricallyconducting film 14 provided for the first substrate 32 or for the secondsubstrate 12 or for any one of the connection terminals, i.e.,electrodes 13, 31 has a thickness, i.e., the electrically conductingfilm 14 provided for the electrodes of the part has a thickness which issmaller than the diameter of the electrically conducting particles 21.

Desirably, furthermore, the electrically conducting terminal 31 of thefirst substrate 32 is composed of ITO, the electrically conductingparticles 21 contained in the anisotropic electrically conductingadhesive 22 provided on the ITO has an average diameter of about 5 μm,the connection terminal portions 13, 31 of the second substrate 200, orthe control circuit for example; IC, arranged being opposed via theanisotropic electrically conducting adhesive 22 forms a copper patternon the substrate, and the electrically conducting film of a solder ortin is formed on the copper pattern by the chemistry of electrolessplating or the electroplating maintaining an average thickness of fromabout 1 μm to about 3 μm.

According to the present invention, the electrically conductingparticles 21 in the anisotropic electrically conducting adhesive agent22 have a diameter that is larger than the thickness of the connectionterminal portion of the substrate to which the electrically conductingconnection is to be made or larger than the thickness of the connectionterminal portion of the part to which the electrically conductingconnection is to be made, so that the electrically conducting particlesare prevented from being buried in the connection terminals and that theelectric conduction is accomplished stably and reliably between theconnection terminal portion of the substrate and the connection terminalportion of the part to which the electrically conducting connection ismade.

By forming the electrically conducting film having a thickness of from 1to 3 μm by the chemistry of electroless plating method or theelectroplating method furthermore, electrically conducting connection isfavorably obtained with respect to the electrically conducting particleshaving an outer diameter of 6 μm.

FIG. 1(B) is a sectional view illustrating a concrete constitution of anelectrically connecting structure of another embodiment of the presentinvention. That is, in a data transfer device 1 constituted by, atleast, a data processing circuit 100 having a connection portion 20equipped with a plurality of electrically conducting terminal groups 31and a drive circuit means, for example IC, 200 which is mounted on thesame glass transparent substrate 32 and separately selects a pluralityof electrically conducting terminals 31 in the data transfer circuit 100and sends predetermined signals to said data processing circuit 100, anelectrically connecting structure S₁ is characterized in that aconnection portion S₁ is formed between the facing connection terminalportions 13 and 31 of the circuits 100 and the driving circuit 200. Onthe other hand, another connecting structure S₂ is formed between theconnection terminal portion 13' of the circuit 200 and the connectionterminal portion 45 formed on the surface of the substrate 32 facingthereto.

At the other end of the electrode 45, a separate connection portion S₃is formed between the electrode 45 and one end portion of an electrode48 arranged on a surface of a separate substrate 250, for example, theFPC or the like, oppositely arranged to the substrate 32.

Further, in this embodiment, the another end of the electrode 48 formedon the FPC 250 is connected to one end of an electrode 47 which isformed on a substrate 36 separately arranged from the substrate 32 toform another separate connection portion S₄.

Note that the electrode 47 formed on a substrate 36, is connected to acentral controlling mean 300 for controlling, for example, the IC 200.

In this embodiment, all of the connection portions S_(l) to S₄ have thesame constructions as to each other and each is identical to theconnection portion S as indicated in FIG. 1(A).

Referring to FIG. 8 illustrating a conventional connection portion inwhich, for example, the FPC is adhered to the liquid crystal displaydevice using an anisotropic electrically conducting adhesive asexplained in the prior art with reference to FIG. 7, electrodes 33 and41 are formed on the opposing surfaces of the pair of substrates 32 to40 that are disposed facing each other, the connection terminal portion31 of the electrode 33 and the connection terminal portion (not shown)of the electrode 41 are disposed on the outside of the sealing portion50, and liquid crystals 60 are sealed inside the sealing portion 50 toconstitute a liquid crystal display device.

A first embodiment of the present invention is illustrated in FIG. 1(A)which is a sectional view along the line A--A of FIG. 7. In FIG. 1(A),the FPC 200 is obtained by providing a copper pattern 13 of a thicknessof 35 μm on the surface of a base film 12 of a polyimide having athickness of about 25 μm on the side to which the electricallyconducting adhesive is to be adhered and by forming an electricallyconducting film 14 of a solder or tin having a thickness of 1 to 3 μm onthe copper pattern 13 by the chemistry of electroless plating or theelectroplating.

On the other hand, the electrically conducting adhesive 22 comprises anepoxy resin or which contains which contains electrically conductingparticles 21 made of solder beads as shown in FIG. 11(A) or plasticbeads 211 with a surface film 212 made of an electrically conductingmaterial.

As shown in FIG. 11(A), the electrically conducting particles 21 aremade of solder without having the surface film. On the other hand, asshown in FIG. 11(B) the particles 21 comprise the plastic beads 211 madeof an epoxy resin or polystyrene resin and the surface thereof iscovered with an electrically conducting layer 212 which is formed byplating nickel thereon and further plating gold on the surface of thenickel plating layer. As mentioned above, the copper pattern electrodes13 are covered with the electrically conducting film 14 made of solder.The solder beads 21 as shown in FIG. 11(A) are also made of solderhaving the melted point being higher than that of the solder used in thefilm 14 to make the solder beads harder than the film 14.

Accordingly, the particles 21 have an outer diameter of about 6 μm.

The anisotropic electrically conducting adhesive 22 have a thickness ofabout 25 μm before it is adhered to the electrodes.

The substrate 32 is obtained by forming the ITO 33 maintaining athickness of about 0.3 μm on a glass substrate having a thickness ofabout 1 mm.

Described below is a method of adhering the FPC 10 as shown in FIG. 2,that corresponds to the second substrate 12 to the substrate 32maintaining electric conduction. The FPC 10 having the anisotropicelectrically conducting adhesive 22 applied onto the connection terminalportion 11 of the FPC 10 is so placed that the anisotropic electricallyconducting adhesive 22 is superposed on the connection terminal portion31 of the substrate 32. Here, a cradle composed of a bakelite or thelike is disposed beneath the-lower surface of the substrate 32, and thesurface of the base film 12 is adhered by the application of heat andpressure from above the connection terminal portion 11 of the FPC 30 byusing a heater as indicated by arrow Y that is shown in FIG. 8.

Here, it is also allowable to employ a method of applying the pressureand heat by pushing up the heater from the lower side.

As shown in FIG. 2, the FPC 10, electrically conducting adhesive 20 andsubstrate 32 were adhered together maintaining electric conduction. Thepressure was from 30 to 40 kg, the heating temperature was from 170° to180° C., and the heating time was from 10 to 15 seconds. The conductionresistance between the FPC 10 and the substrate 32 was about 1.5 Ω whichwas nearly one-half the resistance, about 3 Ω, of the prior art.

Note that, FIG. 2 illustrates a second embodiment of the presentinvention in which the electrically conducting film 14 is provided onthe FPC 10 that is the second substrate 12, and an electricallyconducting film 34 is formed on the ITO 33 of the substrate 32 that isdisposed being opposed to the FPC 10 with the electrically conductingadhesive 22 being held therebetween.

In FIG. 2, the electrically conducting film 14 was formed by chemistryof electroless plating a solder or tin maintaining a thickness of from 1to 3 μm, and the electrically conducting adhesive 22 containingelectrically conducting particles 21 having a diameter of about 6 μm wasused to stably obtain electrical connection in which the electricallyconducting particles 21 were brought into contact with the electricallyconducting film 14 of the FPC 10 and the electrically conducting film 34of the electrodes 33 formed on substrate 32 as a result of the adhesionby the application of heat and pressure.

FIG. 3 illustrates a third embodiment of the present invention in whichthe copper pattern 13 is arranged on the base film 12 of the FPC 10, andis plated with gold maintaining a thickness of 0.03 μm or larger as aprotective electrically conducting film 15 by flash plating in order toprevent the copper pattern 13 from being oxidized.

The electrically conducting film 34 of solder or tin was utilizing thechemistry of electroless plating method having a thickness of from 1 to3 μm on the ITO 33 of the substrate 32 such that the electricallyconducting particles 21 contained in the electrically conductingadhesive 22 were prevented from being buried in the electricallyconducting films 34 and 15. Besides, the electric conduction between thecopper pattern 13 and the ITO 33 is improved by the protectiveelectrically conducting film 15.

FIG. 4 illustrates a fourth embodiment of the present invention inwhich, unlike the FPC explained above, the present invention is adaptedto electrically connecting parts such as ICs to the electricallyconducting pattern on the substrate by using the electrically conductingadhesive 22 which has been utilized in a variety of fields in recentyears. FIG. 4 illustrates the embodiment in which an IC chip 70 that isa part is die-bonded to the substrate 32.

In FIG. 4, the electrically conducting film 34 of solder or tin isplated utilizing the chemistry of electroless plating method,maintaining a thickness of 1 to 3 μm on the ITO 33 on the substrate 32to prevent the electrically conducting particles 21 in the electricallyconducting adhesive 22 from being buried in the electrically conductingfilm 34 and to improve electric conduction between the electrode 71including an electrode made of chromium or copper or bump electrodes,and the ITO 33.

FIG. 5 illustrates a fifth embodiment of the present invention in whichthe IC chip 70 which is a part is die-bonded with an adhesive onto thesubstrate 32.

In FIG. 5, an electrically conducting film 72 of solder or tin is platedutilizing the chemistry of electroless plating method and maintaining athickness of from 1 to 3 μm on the bump electrodes 71 of the IC chip 70.The IC chip 70 is then die-bonded with an adhesive onto the substrate 32preventing the electrically conducting particles 21 from being buried inthe electrically conducting film 72 and improving the electricconduction between the bump electrodes 71 and the ITO 33.

FIG. 6 illustrates a sixth embodiment of the present invention whereinthe IC chip 70 that is a part is die-bonded with an adhesive onto thesubstrate 32.

In FIG. 6, the electrically conducting film 72 of solder or tin isplated utilizing the chemistry of electroless plating method andmaintaining a thickness of from 1 to 3 μm onto the bump electrodes 71 ofthe IC chip 70, and the electrically conducting film 34 of solder or tinis plated utilizing the chemistry of electroless plating method andmaintaining a thickness of from 1 to 3 μm on the ITO 33 of the substrate32. Then, an electrically conducting adhesive is held between theelectrically conducting film 34 and the electrically conducting film 72to accomplish the die-bonding. The electrically conducting particles 21of the electrically conducting adhesive 20 are prevented from beingburied in the electrically conducting films 34 and 72, and the electricconduction is improved between the bump electrodes 71 and the ITO 33.

In the electrically connecting structure 1 of the present invention asdescribed above, it is desired that the electrically conducting films14, 14', 49 and 72 are formed on the surfaces of the opposing electrodes13 and 31, or 33 and 71, or 13' and 45, or 45 and 48 or 48 and 47.

In the electrically connecting structure 1 of the present invention,furthermore, the total thickness of the electrically conducting films14, 14', 49 and 72 formed on the surfaces of the facing electrodes 13and 31, or 33 and 71, or 13' and 45, or 45 and 48 or 48 and 47, must besmaller than the minimum diameter of the electrically conductingparticles 21.

According to the electrically connecting structure 1 of the presentinvention which is subjected to a high pressure and a high temperatureas described above, the electrically conducting particles 21 are partlyfitted into the electrically conducting films 14, 14', 49 and 72 to forma point contact between the electrically conducting particles 21 and theelectrically conducting films 14, 14', 49 and 72, which, then,constitutes part of the electrically conducting passage.

In the electrically connecting structure 1 of the present invention, theelectrically conducting particles 21 are made of hard solder beads, thehardness thereof is higher than that of the film 14 or are composed ofplastic resin beads made of a hard material such as an epoxy resin orpolystyrene resin, and are deformed to some extent by the application ofthe pressure compared to the initial shape between the electrodes in theconnection portion S in the completed electrically connectingstructure 1. The electrically conducting particles 21, however, existbetween the facing electrodes without being crushed. Unlike the priorart, therefore, the electrically conducting particles 21 are not melted,are not substantially deformed to lose their original shapes, and arenot pulverized.

According to the present invention, furthermore, the diameters of theelectrically conducting particles 21 in a direction in which theelectrodes are arranged determine the gap G between the electrodes ofthe connection portion S.

The connected configuration of the electrically connecting structure 1formed between the electrode 13, 33, 31, 71 or 201 or electricallyconducting film 14, 15, 34, or 72 and the electrically conductingparticle 21, will be explained with reference to FIGS. 10, 11(A), 11(B),12(A) and 12(B), hereunder.

When the solder beads are used as the electrically conducting particle21, as shown in FIG. 11(A), the connecting condition in the connectionportion S in the electrically connecting structure 1 of the presentinvention, which is formed between the particle 21 and the electrode 13with the electrically conducting film 14 or the electrode 31 with theelectrically conducting film 34, is illustrated in FIGS. 10 and 12(A).

Note that FIG. 10 shows a plane view of the connection portion S in theelectrically connecting structure 1, while FIG. 12(A) shows a crosssectional view of the connection portion S.

The applicant assumes that the cross-sectional view of the connectionterminal portion of the present invention would probably show aconfiguration as shown in FIG. 12(A), for example, taking theconfiguration of the photograph as shown in FIG. 13, into account.

From FIG. 10, it will be understood that the electrically conductingparticles 21 made of solder, the hardness and melting point of whichbeing higher than those of the solder forming the electricallyconducting film 14, and dispersed in the anisotropic electricallyadhesive film or resin binder 22, are partly contacted to the electrode13 at a narrow point P through the electrically conducting film 14,which is made of solder.

And in FIG. 10, simultaneously a ring-like portion O surrounding theabove-mentioned portion P, is formed and which denotes a part of theelectrically conducting film 14 having a thin thickness.

As understood from FIGS. 10 and 12(A), at an outer peripheral portion ofthe ring-like portion O, there is provided another ring-like portion Qhaving a diameter R.

The ring-like portion Q shows a ring-like deformed portion of theelectrically conducting film 14 which is formed due to a pressing forceapplied to the electrically conducting film 14 caused by the conductingparticle 21 during the heating and the pressing treatment.

FIG. 13 shows a plane view similar to FIG. 10, which is illustrating anactual configuration of the connecting portion between an electrode 13and the particles 21 dispersed in the resin binder 22.

As apparent from FIG. 13, a plurality of the electrically conductingparticle 21 are dispersed in the resin binder 22 and each one of theparticles 21 has a center portion P indicating a portion at which theelectrode 14 and a top surface of the particle 21, made of solder, forexample, while a ring-like portion O which is surrounding the centerportion P.

In accordance with this configuration of the present invention, theparticles 21 and the electrode 13 are strongly brought into contactingto each other so that the conduction resistance can be reduced.

On the other hand, when the particle 211 made of the plastic beads withan electrically conducting film 212 as shown in FIG. 11(B), are used asthe electrically conducting particle 21, the connecting condition in theconnection portion S in the electrically connecting structure 1 of thepresent invention, is shown in FIG. 12(B).

In this embodiment, although the connection portion S is formed betweenthe particle 21 and the electrode 13 with the electrically conductingfilm 14 or the electrode 31 with the electrically conducting film 34, atop portion of the electrically conducting film 212 of the particle 211contacts to the electrode 13 at a narrow point P" through theelectrically conducting film 14, which is made of solder.

And the top portion of the electrically conducting film 212 of theparticle 211 is deformed due to a strong pressure force applied theretoso as to form an electric path between the electrodes 13 and 32 throughthe electrically conducting film 212.

However, in this embodiment, the electrically conducting film 14 is notdeformed to form a projected portion like the one as shown in FIG.12(A).

It is desired that the electrodes 31, 33, 13 and 71 of the presentinvention are made of a material selected from indium tin oxide and thelike.

According to the present invention, the electrically conducting films14, 14', 49 and 72 should be constituted by a material selected fromsolder, tin, nickel, gold, tantalum pentoxide and the like. Theelectrically conducting films 14, 15, 34 and 72 are formed by theelectroplating method or the chemistry of electroless plating method.

In the above-mentioned examples of the present invention, it is furtherdesired that a diameter of the core portion 211 of the particles 21dispersed in the anisotropic electrically conducting resin binder 22,may be 5±1.5 μm and the total diameter thereof including theelectrically conduction film 212 formed on the surface of the coreportion 211, or solder beads may be 6±2 μm.

On the other hand, a ratio of a distribution area of the particles 21 toa predetermined area may be 5 to 20%.

Described below is a method of forming the electrically connectingstructure 1 according to the present invention. That is, in forming aconnection portion between the facing connection terminal portions ofthe circuits or between a connection terminal portion of the circuit anda connection terminal portion of a suitable external input circuit meansfacing thereto in a data transfer device constituted by, at least, adata processing circuit equipped with a plurality of electricallyconducting terminal groups and a drive circuit means connected to aplurality of electrically conducting terminals in the data transfercircuit and sends predetermined signals to said data processing circuit,a method of forming an electrically connecting structure comprising:

a step for preparing a film-like anisotropic electrically conductingadhesive containing electrically conducting particles having diameterslarger than a thickness of an electrically conducting film disposed on asurface of electrodes and applying it at a portion on which a connectionterminal portion will be formed;

a step for disposing the electrodes of said connection portion in amanner facing each other and forming space between said electrodes;

a step for covering the surface of the electrodes of at least one sideof the connection portion with an electrically conducting film having apredetermined thickness;

a step for adjusting the gap of said space in the connection portion bysubjecting said connection portion to the application of heat andpressure, so that the facing electrodes come into direct contact withsaid electrically conducting particles or come into indirect contactwith said electrically conducting particles via said electricallyconducting film.

According to the present invention, it is desired that the electricallyconducting particles 21 have an average diameter of about 5 μm, and theelectrically conducting films 14, 14', 49 and 72 formed on the surfacesof the electrodes have a thickness of from 1 to 3 μm.

According to the present invention, the electrically conductingparticles that are contained in the anisotropic electrically conductingagent to exhibit the action of adhesion while offering electricconduction, are not buried in the electrically conducting films duringthe adhesion with the application of heat and pressure, and exhibittheir function efficiently without losing the electric conduction. Thereis thus obtained stable and reliable electric conduction.

Moreover, the electrically conducting film of solder or tin that isformed by the chemistry of electroless plating helps obtain the productat a reduced cost yet offering improved reliability.

We claim:
 1. In a display panel having a glass substrate and including adata processing circuit having a plurality of electrically conductiveterminals, and a drive circuit having terminal portions facing andspaced from the electrically conductive terminals, the terminal portionsand the conductive terminals thereby providing opposing electrodesspaced by a gap, the data processing circuit and the drive circuit beingformed on the glass substrate, an electrical connecting structurecomprising:an anisotropic electrically conductive adhesive containingelectrically conductive particles and filling the gap between theopposing electrodes, the electrically conductive particles having aminimum diameter; an electrically conductive film coated on a facingsurface of at least one of the opposing electrodes and having a totalthickness; an electrically conductive passage formed between the twoopposing electrodes directly by said electrically conductive particlesand indirectly by the electrically conductive film; and the totalthickness of the electrically conductive film being smaller than theminimum diameter of the electrically conductive particles, so that theelectrically conductive particles cannot be buried in the electricallyconductive film.
 2. In a display panel device including a dataprocessing circuit having a plurality of electrically conductiveterminals and a drive circuit means for sending signals to the dataprocessing circuit, the drive circuit means having terminal portionsfacing and spaced from the electrically conductive terminals, theterminal portions and the conductive terminals thereby providingopposing electrodes spaced by a gap, an electrical connecting structurecomprising:an anisotropic electrically conductive adhesive containingelectrically conductive particles and filling the gap between theopposing electrodes, the electrically conductive particles having aminimum diameter; an electrically conductive film coated on a facingsurface of at least one of the opposing electrodes and having a totalthickness; an electrically conductive passage formed between the twoopposing electrodes directly by said electrically conductive particlesand indirectly by the electrically conductive film; and the totalthickness of the electrically conductive film being smaller than theminimum diameter of the electrically conductive particles, so that theelectrically conductive particles cannot be buried in the electricallyconductive film.
 3. An electrical conducting structure according toclaim 1 or 2, wherein said electrically conductive film is formed on thesurfaces of both of said electrodes that are facing each other.
 4. Anelectrical connecting structure according to claim 3, wherein the totalthickness of the electrically conductive films formed on the surfaces ofboth of said electrodes that are facing each other is smaller than theminimum diameter of said electrically conductive particles.
 5. Anelectrical connecting structure according to claim 1 or 2, wherein saidelectrically conductive particles are partly fitted into saidelectrically conductive film.
 6. An electrical connecting structureaccording to claim 1 or 2, wherein said electrodes are made of amaterial selected from copper, aluminum, and indium oxide.
 7. Anelectrical connecting structure according to claim 1 or 2, wherein saidelectrically conductive film is made of a material selected from solder,tin, nickel, gold, and tantalum pentoxide.
 8. An electrical connectingstructure according to claim 1 or 2, wherein the electrically conductiveparticles mixed in the anisotropic electrically conductive adhesive haveparticles sizes that lie over a range of from 4 to 8 μm.
 9. Anelectrical connecting structure according to claim 1 or 2, wherein saidelectrically conductive particles are mixed in said anisotropicelectrically conductive adhesive in a ratio of distributing area of theparticles to a predetermined area ranging from 5 to 20%.
 10. Anelectrical connecting structure according to claim 1 or 2, wherein saidelectrically conductive particles are composed of a hard material, existbetween the opposing electrodes without being crushed, and the size ofsaid electrically conductive particles determine the gap between theelectrodes of said connection portion.
 11. An electrical connectingstructure according to claim 10, wherein the electrically conductivefilm is partly depressed and deformed by the electrically conductiveparticles about portions where the electrically conductive particles areconnected to the electrode which is covered with said electricallyconductive film, said portions being centers of connection between saidelectrically conductive particles and said electrode.